Body oxygen stores, aerobic dive limits and diving behaviour of the star-nosed mole (Condylura cristata) and comparisons with non-aquatic talpids.

The dive performance, oxygen storage capacity and partitioning of body oxygen reserves of one of the world's smallest mammalian divers, the star-nosed mole Condylura cristata, were investigated. On the basis of 722 voluntary dives recorded from 18 captive star-nosed moles, the mean dive duration (9.2+/-0.2 s; mean +/- S.E.M.) and maximum recorded dive time (47 s) of this insectivore were comparable with those of several substantially larger semi-aquatic endotherms. Total body O(2) stores of adult star-nosed moles (34.0 ml kg(-1)) were 16.4 % higher than for similarly sized, strictly fossorial coast moles Scapanus orarius (29.2 ml kg(-1)), with the greatest differences observed in lung and muscle O(2) storage capacity. The mean lung volume of C. cristata (8.09 ml 100 g(-1)) was 1.81 times the predicted allometric value and exceeded that of coast moles by 65.4 % (P=0.0001). The overall mean myoglobin (Mb) concentration of skeletal muscles of adult star-nosed moles (13.57+/-0.40 mg g(-1) wet tissue, N=7) was 19.5 % higher than for coast moles (11.36+/-0.34 mg g(-1) wet tissue, N=10; P=0.0008) and 54.2 % higher than for American shrew-moles Neurotrichus gibbsii (8.8 mg g(-1) wet tissue; N=2). The mean skeletal muscle Mb content of adult star-nosed moles was 91.1 % higher than for juveniles of this species (P<0.0001). On the basis of an average diving metabolic rate of 5.38+/-0.35 ml O(2) g(-1) h(-1) (N=11), the calculated aerobic dive limit (ADL) of star-nosed moles was 22.8 s for adults and 20.7 s for juveniles. Only 2.9 % of voluntary dives by adult and juvenile star-nosed moles exceeded their respective calculated ADLs, suggesting that star-nosed moles rarely exploit anaerobic metabolism while diving, a conclusion supported by the low buffering capacity of their skeletal muscles. We suggest that a high mass-specific O(2) storage capacity and relatively low metabolic cost of submergence are key contributors to the impressive dive performance of these diminutive insectivores.